Stocks could come under more pressure Friday as investors grow anxious about the crisis in Ukraine and the state of the Chinese economy.

But global markets, which often lead Wall Street, were in the red as U.S. and Russian officials met in London to try to find a diplomatic solution to an increasingly tense stand-off over the fate of the Ukrainian region of Crimea.

Investors are bracing themselves for Sunday's referendum in Crimea, where voters will decide whether to break away from Ukraine and join Russia. Ukraine and the West have described the vote as illegal. They have accused Russia of violating Ukraine's sovereignty and are threatening sanctions.

Russia's benchmark share index fell more than 2%, taking losses for the year so far to nearly 19%, and the ruble weakened further against the dollar. Russian markets have been hit hard by fears that the crisis will deter foreign investment and wipe out growth this year.

U.S. stocks fell Thursday on worries about global tensions and more bad economic news out of China. The Dow fell more than 230 points while the S&P 500 and Nasdaq were off by more than 1%.